Conveyors of various types are well known for handling bulk particulate materials. Belted conveyors, in which an endless belt is transported around a plurality of troughing roller and idler roller assemblies, are frequently used for transporting abrasive materials. Screw conveyors and bucket conveyors can be used to transport freely flowing materials and can move such materials vertically. Linked and paddle type conveyors of various configurations can be used to move bulk particulate materials at steeper inclinations than are possible for belted conveyors.
Stockpiles of bulk particulate materials may be created using stacking conveyors which are designed to drop the materials off an elevated discharge end. The amount of material that can be placed in a stockpile by a stacking conveyor depends in part on the length of the conveyor and on the elevation of its discharge end. Furthermore, a stacking conveyor that is adapted to pivot about its feed end in a radial direction can stockpile a much greater quantity of bulk particulate materials than can one that is fixed against radial movement.
When bulk material handling needs at a particular site are temporary, it is desirable to use a portable stacking conveyor. In order for such a conveyor to be of sufficient length and elevation to be useful and short enough to be transportable over public roads, it must be capable of being configured between an extended operating configuration and a shortened transport configuration. U.S. Pat. No. 4,135,614 of Penterman and U.S. Pat. No. 5,515,961 of Murphy et al. describe portable radial stacking conveyors comprising a center section and a pair of folding end sections that fold over the center section for transport and unfold for operation. U.S. Pat. No. 6,186,311 of Conner describes a portable conveyor system comprising a pair of folding stacking conveyors and a pair of transport conveyors. The stacking conveyors are folded and disposed side by side for transport with the transport conveyors removably mounted atop the folded stacking conveyors. U.S. Pat. No. 6,056,252 of Johannsen and U.S. Pat. No. 6,360,876 of Nohl et al. describe portable stacking conveyors which include a primary conveyor that is adapted to receive a secondary conveyor in telescoping fashion and means for moving the secondary conveyor longitudinally with respect to the primary conveyor between a retracted position and an extended position. U.S. Pat. No. 6,929,113 of Hoover et al. describes a portable radial stacking conveyor having a primary conveyor frame and a telescoping secondary conveyor frame, both of which support a single conveyor belt having a single drive mechanism. U.S. Pat. No. 5,203,442 of Oury et al. describes a cantilever conveyor for concrete which includes a single belt supported by a primary frame, a secondary frame and a tertiary frame. The secondary frame is mounted so as to telescope from the primary frame, and the tertiary frame is mounted so as to telescope from the secondary frame.
It is desirable to have a portable stacking conveyor that can be placed in an operating configuration that is as long as possible but which can also be placed in a transport configuration that is short enough and light enough to be transportable over public roads. In a portable stacking conveyor comprising a primary conveyor (or primary conveyor frame) and a telescoping secondary conveyor (or secondary conveyor frame), the difference between its length in the operating configuration and its length in the travel configuration depends in part on the support mechanism by which the primary conveyor (or primary conveyor frame) supports the secondary conveyor (or secondary conveyor frame) when extended. In the assembly of U.S. Pat. No. 6,056,252, a dual support assembly is provided, in which the bottom chord of the secondary (or extensible) conveyor frame is supported by a first support assembly located at the rear end of the primary conveyor frame, while the top chord of the secondary conveyor frame is supported by a second support assembly spaced from the first support assembly towards the front end of the primary conveyor frame. In the assembly of U.S. Pat. No. 6,929,113, a first roller assembly located on the lower portion of the primary conveyor frame at the rear end supports the bottom chord of the secondary conveyor frame, and a second roller assembly located on the top chord of front end of the secondary conveyor frame bears against an upper beam of the primary conveyor frame.